In manufacturing semiconductor devices, various processing apparatuses are used to subject a target substrate, such as a semiconductor wafer, to processes, such as CVD (Chemical Vapor Deposition), oxidation, diffusion, reformation, annealing, and etching. As processing apparatuses of this kind, vertical heat processing apparatuses are known to subject a number of wafers together to a heat process. In general, vertical heat processing apparatuses have a vertical airtight reaction tube (process chamber) for accommodating wafers. The reaction tube has a load port formed at the bottom, which is selectively opened and closed by a lid moved up and down by an elevator. Within the reaction tube, the wafers are supported at intervals in the vertical direction on a holder called a wafer boat. The wafer boat is loaded and unloaded to and from the reaction tube through the load port by the elevator while the wafer boat holds the wafers and is supported on the lid.
In vertical heat processing apparatuses, metal contamination may occur such that a metal impurity is mixed into a thin film on the wafer surface, although it is in a very small amount. With the increase in the degree of density and integration of semiconductor devices, the thickness of films in the semiconductor devices is becoming smaller, and the device characteristics become more sensitive to metal contamination. Accordingly, it is necessary to take countermeasures against such metal contamination in order to improve the device characteristics. In this respect, the present inventors have found that this metal contamination is associated with metal impurities contained in quartz products, such as reaction tubes, wafer boats, and thermal insulation cylinders for supporting wafer boats.